Running lateralward and downward, it is inserted by a thin, flat tendon into the lateral side of the base of the first phalanx of the thumb and the capsule of the metacarpophalangeal joint.

Innervation

The abductor pollicis brevis is innervated by the recurrent branch of the median nerve. C8/T1

Actions

Abduction of the thumb is defined as the movement of the thumb anteriorly, a direction perpendicular to the palm. The abductor pollicis brevis does this by acting across both the carpometacarpal joint and the metacarpophalangeal joint.